Sparking plug

ABSTRACT

A sparking plug comprising a metal tubular housing, a housing electrode provided on a portion of said housing, a central electrode which is mounted within and spaced from the housing and extends axially thereof, the central and housing electrodes being separated from each other by a spark gap, and an annular, translucent insulator which is mounted within and sealed to the housing and is subject to compression by the latter, the central electrode extending through and being sealed to the insulator, the coefficient of thermal expansion of the housing, throughout a predetermined temperature range, being substantially greater than that of the insulator.

United States Patent 1191 Thring Nov. 5, 1974 [54] SPARKING PLUG M13389 3 413 501111 313/129 2,04 ,302 l 6 ardell 313/145 X [75] Inventor. John Meredith Thrlng, Woodford 2,172,548 2/1939 schwamkopf 313/141I X Green, England 2,217,825 10/1940 Twining et al 313/141.1 x Assignee: Gunsonas Colorplugs Clayton London, England Przmary Examiner-Alfred L. Brody Flledl J 1973 Attorney, Agent, or Firm-Cushman, Darby & [21 Appl. No.: 320,844 Cushman [30] Foreign Application Priority Data [57] AFSIRACT Jan 19 1972 Great Britain 2548/72 A sparking plug comprising a metal tubular housmg, a

' housing electrode provided on a portion of said housing, a central electrode which is mounted within and [52] Cl 313/118 0 2 0 spaced from the housing and extends axially thereof, [51] Int Cl Holt 13/12 Holt 13/20 6 13/38 the central and housing electrodes being separated [58] Field oi Search 313/143 129 135 141.1 fmm P l annular trans" 313/145 118 145 3 6 E lucent lnsulator which is mounted w1th1n and sealed to P 169 169 the housing and is subject to compression by the latter, the central electrode extending through and being [56] References Cited sealed to the insulator, the coefficient of thermal expansion of the housing, throughout a predetermined UNITED STATES PATENTS temperature range, being substantially greater than l,l96,566 8/1916 McDowell 313/145 X th t of the in lat r 1,347,367 7/1920 Gerbaud 313/1451 1,554,996 9/1925 Flynt 313/129 x 10 Claims, 8 Drawing gures SPARKING PLUG This invention concerns a sparking plug.

According to the present invention, there isprovided a sparking plug comprising a metal tubular housing a portion of which is provided with or constitutes a housing electrode, a central electrode which is mounted within and spaced from the housing and extends axially thereof, the central and housing electrodes being separated from each other by a spark gap, and an annular, translucent insulator which is mounted within and sealed to the housing and is subjected to compression by the latter, the central electrode extending through and being sealed to the insulator, the coefficient of thermal expansion of the housing, throughout a predetermined temperature range, being substantially greater than that of the insulator.

The term translucent" insulators as used herein is intended to be broad enough to include insulators which are transparent. Indeed, these are the preferred insulators.

The central electrode may extend through and may be sealed to the interior of a hollow cylindrical insulator which is itself mounted within and sealed to the translucent insulator, the hollow cylindrical insulator extending outwardly of the translucent insulator.

The hollow cylindrical member may be made of ceramic material.

The hollow cylindrical insulator may be sealed to the central electrode by means of a glass member.

The coefficient of thermal expansion of the translucent insulator is preferably substantially the same as that of the central electrode throughout the said predetermined temperature range.

The translucent insulator is preferably a transparent glass disc. Moreover the housing preferably extends axially beyond each of the opposite faces of the disc.

The housing may be of one part construction. Alternatively, the portion of the housing which is formed or provided with the housing electrode may be detachably connected to the portion of the housing provided with the insulator. In the latter case, the portion of the housing provided with the housing electrode may be threaded into the other portion and may have a noncylindrical internal surface for engagement by a tool.

The housing may be provided with a housing electrode which is non-integral with and extends radially inwardly of the housing.

Alternatively, the housing electrode may be integral with the housing, the central electrode having a radially extending end portion which is separated from the housing electrode by the said spark gap.

The invention is illustrated merely by way of example, in the accompanying drawings, in which:-

FIG. 1 is a sectional view of a first embodiment of a sparking plug according to the present invention, the said first embodiment having a one-piece housing,

FIG. 2 is a plan view of the sparking plug of FIG. 1,

FIG. 3 is a sectional view of one part of a second embodiment of a sparking plug according to the present invention, the said second embodiment having a twopiece housing,

FIG. 4 is a plan view of the part shown in FIG. 3.

FIG. 5 is a sectional view of the other part of the said second embodiment,

FIG. 6 is a plan view of the said other part, and

FIGS. 7 and 8 are respectively sectional views of a thrid embodiment and a fourth embodiment of a sparking plug according to the present invention.

Referring first to FIGS. 1 and 2, a sparking plug comprises a metal tubular housing 10 having an externally threaded cylindrical portion 11 which is adapted to be screwed into a threaded hole in the casing of an internal combustion engine (not shown). The portion 11 is provided with a non-integral housing electrode 12 which extends radially inwardly of the housing.

A central electrode 13 is mounted within and spaced from the housing 10 and extends axially of the latter. The central electrode 13 and the housing electrode 12 are separated from each other by a spark gap 14.

The housing 10, at its end remote from the interior of the engine, has a hexagon shaped part 15 within which is mounted and to which is sealed an annular transparent glass insulator disc 16. The central electrode 13 extends centrally through and is sealed to the insulator disc 16.

The coefficient of thermal expansion of the housing 10, throughout the whole of the operating temperature range is substantially greater than that of the insulator disc 16, while the coefficient of thermal expansion of the insulator disc 16 is substantially the same as that of the central electrode 13 throughout the said operating temperature range. Thus, for example, the coefficient of thermal expansion at of the housing 10 may be in the range 130 to I60' lO" /C, while the coefficient of ther mal expansion of both the insulator disc 16 and the central electrode 13 may be in the range of to I05. l0"/C.

The housing may for example be made of a lead-free mild steel, e.g., a low carbon steel known as E.N. 1A, while the glass of the insulator disc 16 may be a sintered borosilicate glass. The central electrode 13 may be made of an iron-nickel alloy.

The insulator disc 16 is subjected to compression by the housing 10, throughout the operating temperature range, e.g., by shrinking the housing 10 onto the insulator disc 16. By reason of this compression and of the selection of the above-mentioned coefficients of thermal expansion, hermetic seals are achieved between the central electrode 13 and the insulator disc 16, and between the insulator disc 16 and the housing 10, without the use of any special sealing compounds, while the risk that the glass of the insulator disc 16 will crack is reduced.

The said hermetic seals have great physical strength by reason of the fact that glass is stronger in compression than in tension. Before the glass can be cracked or ruptured, the compressive stresses purposely introduced must be overcome.

As will be seen from FIG. 1, the part 15 of the housing 10 extends axially beyond each of the opposite faces 20, 21 of the insulator disc 16. This construction is provided to avoid disturbing fringe effects.

As will be appreciated, in a sparking plug as shown in FIGS. 1 and 2, the combustion which occurs on sparking can be viewed axially through the insulator disc 16, which may be quite thin, and the colour of this combustion will be indicative of the combustion characteristics within the respective cylinder of the engine.

In FIGS. 3 to 6, there is shown a sparking plug having a housing made up of detachably interconnected portions 22, 23. The portion 22, which is of hexagon shape, has mounted within and sealed to it an annular 3 transparent glass insulator disc 24 extending axially through which there is mounted a central electrode 25. As in the case of the construction of FIGS. 1 and 2, the coefficient of thermal expansion of the portion 22 is, throughout the operating temperature range, substantially greater than that of the insulator disc 24, while the coefficient of thermal expansion of the insulator disc 24 is substantially the same as that of the central electrode 25 throughout the operating temperature range.

The portion 22 is internally threaded at 26 and into it is threaded an externally threaded portion 30 of the portion 23. The portion 30 is provided with a nonintegral housing electrode 31 which extends radially inwardly of the portion 23 and is separated by a spark gap from the central electrode 25.

The portion 23 is also provided with an externally threaded cylindrical portion 32 to enable it to be screwed into the casing of an internal combustion engine (not shown). The portion 32 has a non-cylindrical internal surface 33 for engagement by a tool so as to enable the portions 22, 23 to be detachably connected to and disconnected from each other.

In FIG. 7 is shown a sparking plug 34 which is generally'similar to that of FIGS. I and 2 and which for this reason will not be described in detail, like reference numerals indicating like parts.

In the FIG. 7 construction, however, a non-integral housing electrode 12 is not provided, the end portion of the cylindrical portion 11 constituting an integral housing electrode. The central electrode 13, moreover, has a radially extending end portion 35 which is separated from the said housing electrode by the spark gap 14.

In FIG. 8 there is shown a sparking plug 36 which is generally similar to that of FIG. 7 and which for this reason will not be described in detail, like reference numerals indicating like parts.

Inv the FIG. 8 construction, however, the central electrode 13 extends through and is sealed to the interior of a thin walled alumina or other ceramic hollow cylindrical insulator 37 by means of an annular glass block 40 which may be either transparent or opaque. The hollow cylindrical insulator 37 is mounted within and sealed to an annular transparent glass insulator disc 41, the latter being mounted within and sealed to the metal housing 10. If the glass employed in the block 40 is transparent, it may be the same as that of the disc 41.

The hollow cylindrical insulator 37 and the glass block 40 extend outwardly of the disc 41 and in the embodiment shown, have axial lengths about three times the thickness of the disc 41. Thus the construction shown in FIG. 8 increases the tracking length, i.e., the length of a short circuit between the high voltage central electrode 13 and the earthed metal housing 10. Thus the construction assists in preventing tracking over the disc 41 when the conditions at the spark gap 14 causes the voltage to rise to an unusually high level before breakdown at the spark gap occurs.

I claim:

1. A sparking plug comprising a metal tubular housing, a housing electrode provided on a portion of said housing, a metal central electrode which is mounted within and spaced from the housing and extends axially thereof, the central and housing electrodes being made of different metals and being separated from each other by a spark gap, and an annular, translucent insulator disc which is mounted within the housing and is subjected to radial compression by the latter to effect sealing therebetween, the central electrode extending through and being sealed to the insulator disc. the coefficient of thermal expansion of the housing, throughout a predetermined temperature range, being substantially greater than that of the insulator disc. and the coefficient of thermal expansion of the insulator disc being substantially the same as that of the central electrode throughoutthe said predetermined temperature range.

2. A sparking plug comprising a metal tubular housing, a housing electrode provided on a portion of said housing, the portion of the housing which has the housing electrode being detachably connected to the portion of the housing provided with the insulator a central electrode which is mounted within and spaced from the housing and extends axially thereof, the central and housing electrodes being separated from each other by a spark gap, and an annular, translucent insulator which is mounted within and sealed to the housing and is subjected to radial compression by the latter, the central electrode extending through and being sealed to the translucent insulator, the coefficient of thermal expansion of the housing, throughout a predetermined temperature range, being substantially greater than that of the translucent insulator.

3. A sparking plug as claimed in claim 1 in which the central electrode extends through and is sealed tothe interior of a hollow cylindrical insulator disc which is itself mounted within and sealed to the translucent insulator, the hollow cylindrical insulator extending outwardly of the translucent insulator disc.

4. A sparking plug as claimed in claim 3 in which the hollow cylindrical insulator is made of ceramic material.

5. A sparking plug as claimed in claim 3 in which the hollow cylindrical insulator is sealed to the central electrode by means of a glass member.

6. A sparking plug as claimed in claim 1 in which the translucent insulator disc is a transparent glass disc.

7. A sparking plug as claimed in claim 6 in which the housing extends axially beyond each of the opposite faces of the disc.

8. A sparking plug as claimed in claim 2 in which the portion of the housing which has the housing electrode is threaded into the other portion and has a noncylindrical internal surface for engagement by a tool to facilitate relative separation of said portions.

9. A sparking plug as claimed in claim 1 in which the housing is provided with a housing electrode which is non-integral with and extends radially inwardly of the housing.

10. A sparking plug as claimed in claim 1 in which the housing electrode is integral with the housing, the central electrode having a radially extending end portion which is separated from the housing electrode by the spark gap. 

1. A sparking plug comprising a metal tubular housing, a housing electrode provided on a portion of said housing, a metal central electrode which is mounted within and spaced from the housing and extends axially thereof, the central and housing electrodes being made of different metals and being separated from each other by a spark gap, and an annular, translucent insulator disc which is mounted within the housing and is subjected to radial compression by the latter to effect sealing therebetween, the central electrode extending through and being sealed to the insulator disc, the coefficient of thermal expansion of the housing, throughout a predetermined temperature range, being substantially greater than that of the insulator disc, and the coefficient of thermal expansion of the insulator disc being substantially the same as that of the central electrode throughout the said predetermined temperature range.
 2. A sparking plug comprising a metal tubular housing, a housing electrode provided on a portion of said housing, the portion of the housing which has the housing electrode being detachably connected to the portion of the housing provided with the insulator a central electrode which is mounted within and spaced from the housing and extends axially thereof, the central and housing electrodes being separated from each other by a spark gap, and an annular, translucent insulator which is mounted within and sealed to the housing and is subjected to radial compression by the latter, the central electrode extending through and being sealed to the translucent insulator, the coefficient of thermal expansion of the housing, throughout a predetermined temperature range, being substantially greater than that of the translucent insulator.
 3. A sparking plug as claimed in claim 1 in which the central electrode extends through and is sealed to the interior of a hollow cylindrical insulator disc which is itself mounted within and sealed to the translucent insulator, the hollow cylindrical insulator extending outwardly of the translucent insulator disc.
 4. A sparking plug as claimed in claim 3 in which the hollow cylindrical insulator is made of ceramic material.
 5. A sparking plug as claimed in claim 3 in which the hollow cylindrical insulator is sealed to the central electrode by means of a glass member.
 6. A sparking plug as claimed in claim 1 in which the translucent insulator disc is a transparent glass disc.
 7. A sparking plug as claimed in claim 6 in which the housing extends axially beyond each of the opposite faces of the disc.
 8. A sparking plug as claimed in claim 2 in which the portion of the housing which has the housing electrode is threaded into the other portion and has a non-cylindrical internal surface for engagement by a tool to facilitate relative separation of said portions.
 9. A sparking plug as claimed in claim 1 in which the housing is provided with a housing electrode which is non-integral with and extends radially inwardly of the housing.
 10. A sparking plug as claimed in claim 1 in which the housing electrode is integral with the housing, the central electrode having a radially extending end portion which is separated from the housing electrode by the spark gap. 